Plasmonic filters comprise a pattern made of a dielectric material extending through a metal layer or conversely, the pattern being generally periodically repeated in the layer.
Patent application WO 2010/029097 (incorporated by reference) describes an example of a plasmonic filter comprising a cross-shaped pattern made of a dielectric material periodically repeated in a metal layer. This filter is of narrow bandpass type, that it, the wavelength range for which the filter enables more than 50% of the received light to pass has a width smaller than some hundred nanometers.
In certain applications, particularly in the field of image sensors, when a high-pass filter blocking visible light and transparent to infrared light is desired to be formed, a layer of a material, currently called black resin, absorbing visible light and transparent to infrared light is used. However, the use of black resin raises various issues, particularly due to the fact that black resin is altered when submitted to temperatures higher than 250° C., which makes the forming of other structures implying thermal treatments difficult once the black resin has been deposited. Further, it is difficult to delimit black resin on small surfaces corresponding to elementary pixels.
It would thus be desirable to have a high-pass filter transparent to infrared light and blocking visible light, which uses no absorbing layer of black resin type.